The present invention relates to a television receiver including a system for identifying and extracting auxiliary digital data, having one of a plurality of formats, inserted in the vertical blanking interval of a television video signal.
Currently, auxiliary data, such as, for example, closed captioning information and extended data service (XDS) information, is transmitted in digital form during the vertical blanking interval of standard television signals. The closed captioning information represents the closed caption characters, and XDS information includes a variety of auxiliary data. This information is inserted in known locations in the vertical blanking interval of the television video signal and formatted in a known manner. In the NTSC television signal in the United States, line 21 in field 1 is reserved for closed captioning information, and line 21 of field 2 is reserved for XDS information.
Referring to FIG. 1, the closed captioning signal is illustrated in the second waveform from the top, labeled CC SIG. This signal includes a first interval of 10.5 microseconds (xcexcs) in which the signal remains nominally at 0 IRE amplitude. This is followed by a clock run-in interval of 14 xcexcs containing seven cycles of a 500 kHz sine wave clock signal having a peak-to-peak amplitude which is the same as the closed captioning data, which follows. The peak-to-peak amplitude is nominally 50 IRE. The run-in interval is followed by a 3 xcexcs period of 0 IRE signal. After the 3 xcexcs 0 IRE signal interval, a start bit of 2 xcexcs duration occurs, followed by 16 data bit intervals, each also of 2 xcexcs duration, in which data is transmitted in a non-return-to-zero (NRZ) format. In this manner, two bytes of closed captioning information is transmitted. A closed captioning processor in a receiver extracts the closed captioning data from its location in the vertical blanking interval and displays that information on the television display device.
Digital auxiliary information other than closed captioning and XDS information may also be transmitted in the vertical blanking interval, using the same format, for example, television program scheduling information. A scheduling service has been provided by Star-sight company in which scheduling information was transmitted in the vertical blanking interval of the video signal, using the same format as the closed caption information. A scheduling processor in a receiver extracts the scheduling data from its location in the vertical blanking interval and displays that information, allowing the viewer to make TV program selections based on the displayed scheduling data. Recently, however, another format for auxiliary digital data, specifically TV program scheduling data, has been proposed by Gemstar company.
No location in the vertical blanking interval has been reserved for the Star-sight or Gemstar scheduling information. Thus, different broadcasters are free to include it in any location in the vertical blanking interval, except those locations (lines 21 in fields 1 and 2) reserved for closed captioning information and XDS information. Also, data transmitted in the proposed Gemstar system, may at times be in the closed caption format, described above, and at other times be in a newly proposed format, termed the Gemstar format in the remainder of this application.
The Gemstar format signal is illustrated in FIG. 1 as the third waveform from the top, labeled GS SIG. A Gemstar format line in the vertical blanking interval also starts with 10.5 xcexcs of nominally 0 IRE signal. But that interval is followed by only 5 cycles of a 500 kHz, nominally 50 IRE peak-to-peak, sine wave run-in clock signal. The run-in clock signal is immediately followed by a digital nine bit frame identifying code having the predetermined value of 011101101. Each bit in the frame code takes 1 xcexcs, and is in NRZ format. The frame code is immediately followed by 32 data bits, each also taking 1 xcexcs, in NRZ format. In this manner four bytes of scheduling data is transmitted in the closed captioning location in the vertical blanking interval. Again, a scheduling processor in the receiver extracts the scheduling data from its location in the vertical blanking interval and allows the viewer to make selections based on the scheduling data.
It is desirable to provide an auxiliary information decoder that reliably decodes multiple auxiliary data formats such as both Gemstar format data and closed caption data. One problem that can arise when decoding auxiliary data is that signal noise can cause data to be decoded incorrectly. For example, noise may cause one or more bits of a frame code to be incorrect. As a result, a frame code detector may process a frame code containing noise-related errors and indicate incorrectly the type of data that exists in a particular portion of a television signal. For example, a decoder processing a Gemstar frame code containing erroneous bits may indicate incorrectly that the line interval associated with the frame code does not contain Gemstar data. As a result, the decoder may ignore the line interval rather than decode the data as desired.
In accordance with principles of the present invention, an auxiliary digital data extractor in a television receiver processes a composite video signal including auxiliary digital data components which have either a first frame code having a predetermined number of bits and auxiliary data in a first format, or a second frame code having the same number of bits and auxiliary data in a second format. A frame code detector is responsive to one subset of the frame code bits to detect the first frame code and to a different subset of frame code bits to detect the second frame code. An auxiliary data utilization circuit receives auxiliary data in the either first format when the first frame code is detected or the second format when the second frame code is detected.
In accordance with another aspect of the invention, an auxiliary information decoder has a first mode of operation for detecting any occurrence of auxiliary information in a signal and a second mode of operation for detecting a particular occurrence of auxiliary information in the signal.